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Date:   Fri, 20 Nov 2020 10:34:50 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Sumit Semwal <sumit.semwal@...aro.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        Christian Koenig <christian.koenig@....com>,
        lkml <linux-kernel@...r.kernel.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...nel.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Ørjan Eide <orjan.eide@....com>,
        Robin Murphy <robin.murphy@....com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Simon Ser <contact@...rsion.fr>,
        James Jones <jajones@...dia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 0/7] dma-buf: Performance improvements for system heap
 & a system-uncached implementation

On Fri, Nov 20, 2020 at 7:32 AM Sumit Semwal <sumit.semwal@...aro.org> wrote:
>
> Hi Daniel,
>
>
> On Wed, 18 Nov 2020 at 13:16, Daniel Vetter <daniel@...ll.ch> wrote:
> >
> > On Wed, Nov 18, 2020 at 3:40 AM John Stultz <john.stultz@...aro.org> wrote:
> > > On Fri, Nov 13, 2020 at 12:39 PM Daniel Vetter <daniel@...ll.ch> wrote:
> > > > On Thu, Nov 12, 2020 at 08:11:02PM -0800, John Stultz wrote:
> > > > > On Thu, Nov 12, 2020 at 1:32 AM Daniel Vetter <daniel@...ll.ch> wrote:
> > > > > > On Thu, Nov 12, 2020 at 11:09:04AM +0530, Sumit Semwal wrote:
> > > > > > > On Tue, 10 Nov 2020 at 09:19, John Stultz <john.stultz@...aro.org> wrote:
> > > > > > > >
> > > > > > > > Hey All,
> > > > > > > >   So just wanted to send my last revision of my patch series
> > > > > > > > of performance optimizations to the dma-buf system heap.
> > > > > > >
> > > > > > > Thanks very much for your patches - I think the first 5 patches look good to me.
> > > > > > >
> > > > > > > I know there was a bit of discussion over adding a new system-uncached
> > > > > > > heap v/s using a flag to identify that; I think I prefer the separate
> > > > > > > heap idea, but lets ask one last time if any one else has any real
> > > > > > > objections to it.
> > > > > > >
> > > > > > > Daniel, Christian: any comments from your side on this?
> > > > > >
> > > > > > I do wonder a bit where the userspace stack for this all is, since tuning
> > > > > > allocators without a full stack is fairly pointless. dma-buf heaps is a
> > > > > > bit in a limbo situation here it feels like.
> > > > >
> > > > > As mentioned in the system-uncached patch:
> > > > > Pending opensource users of this code include:
> > > > > * AOSP HiKey960 gralloc:
> > > > >   - https://android-review.googlesource.com/c/device/linaro/hikey/+/1399519
> > > > >   - Visibly improves performance over the system heap
> > > > > * AOSP Codec2 (possibly, needs more review):
> > > > >   - https://android-review.googlesource.com/c/platform/frameworks/av/+/1360640/17/media/codec2/vndk/C2DmaBufAllocator.cpp#325
> > > > >
> > > > > Additionally both the HiKey, HiKey960 grallocs  and Codec2 are already
> > > > > able to use the current dmabuf heaps instead of ION.
> > > > >
> > > > > So I'm not sure what you mean by limbo, other than it being in a
> > > > > transition state where the interface is upstream and we're working on
> > > > > moving vendors to it from ION (which is staged to be dropped in 5.11).
> > > > > Part of that work is making sure we don't regress the performance
> > > > > expectations.
> > > >
> > > > The mesa thing below, since if we test this with some downstream kernel
> > > > drivers or at least non-mesa userspace I'm somewhat worried we're just
> > > > creating a nice split world between the android gfx world and the
> > > > mesa/linux desktop gfx world.
> > > >
> > > > But then that's kinda how android rolls, so *shrug*
> > > >
> > > > > > Plus I'm vary of anything related to leaking this kind of stuff beyond the
> > > > > > dma-api because dma api maintainers don't like us doing that. But
> > > > > > personally no concern on that front really, gpus need this. It's just that
> > > > > > we do need solid justification I think if we land this. Hence back to
> > > > > > first point.
> > > > > >
> > > > > > Ideally first point comes in the form of benchmarking on android together
> > > > > > with a mesa driver (or mesa + some v4l driver or whatever it takes to
> > > > > > actually show the benefits, I have no idea).
> > > > >
> > > > > Tying it with mesa is a little tough as the grallocs for mesa devices
> > > > > usually use gbm (gralloc.gbm or gralloc.minigbm). Swapping the
> > > > > allocation path for dmabuf heaps there gets a little complex as last I
> > > > > tried that (when trying to get HiKey working with Lima graphics, as
> > > > > gbm wouldn't allocate the contiguous buffers required by the display),
> > > > > I ran into issues with the drm_hwcomposer and mesa expecting the gbm
> > > > > private handle metadata in the buffer when it was passed in.
> > > > >
> > > > > But I might take a look at it again. I got a bit lost digging through
> > > > > the mesa gbm allocation paths last time.
> > > > >
> > > > > I'll also try to see if I can find a benchmark for the codec2 code
> > > > > (using dmabuf heaps with and without the uncached heap) on on db845c
> > > > > (w/ mesa), as that is already working and I suspect that might be
> > > > > close to what you're looking for.
> > > >
> > > > tbh I think trying to push for this long term is the best we can hope for.
> > > >
> > > > Media is also a lot more *meh* since it's deeply fragmented and a lot less
> > > > of it upstream than on the gles/display side.
> > > >
> > > > I think confirming that this at least doesn't horrible blow up on a
> > > > gralloc/gbm+mesa stack would be useful I think.
> > >
> > > Sorry, I'm still a little foggy on precisely what you're suggesting here.
> > >
> > > The patch stack I have has already been used with db845c (mesa +
> > > gbm_grallloc), with the codec2 (sw decoders) using dmabuf heaps.
> > > So no blowing up there. And I'm working with Hridya to find a
> > > benchmark for codec2 so we can try to show the performance delta.
> > >
> > > However, if you're wanting a dma-buf gralloc implementation with mesa,
> > > that may be a little tougher to do, but I guess I can give it a go.
> > >
> > > Hopefully this will address concerns about the system-uncached heap
> > > patch (the last two patches in this series)?
> > >
> > > In the meantime I hope we can queue the first five patches, as it
> > > would be nice to get the code rearranging in as there are others
> > > trying to stage their own heaps, and I'd like to avoid dragging that
> > > churn out for too long (in addition to improving the allocation
> > > performance). Those changes have no ABI implications.
> >
> > Maybe I'm also misunderstanding what dma-buf heaps is used for in
> > Android, at least usually. I thought it's used to allocate all the
> > winsys/shared buffers through gralloc (at least in the blobby stacks),
> > to handle the allocation constraints problem. In the open stacks we
> > don't seem to have a platform with both mesa and v4l (or some other
> > codec) with "interesting" allocations constraints, so no one using
> > that gralloc+dma-buf heaps combo for what it was meant for. Hence why
> > I'm a bit vary that we're creating something here which just misses
> > the point a bit when we try to actually use it (in that glorious
> > forever-future world where an android platform has enough drivers in
> > upstream to do so).
> >
> > For other "this solves a system problem" we tend to be quite a bit
> > more picky with the demonstration use case, to make sure we're
> > actually creating something that solves the problem in reality.
> >
> > But it also looks like Android's just not there yet, so *shrug* ...
>
> For me, looking at the first 5 patches (listed below, for quick
> reference), they are only doing code reorganisation and minor updates
> for already existing heaps, and no ABI change, I am not able to
> clearly see your objection here. To me, these seem to be required
> updates that the existing system heap users can benefit from.
>
> dma-buf: system_heap: Rework system heap to use sgtables instead of
>     pagelists
>   dma-buf: heaps: Move heap-helper logic into the cma_heap
>     implementation
>   dma-buf: heaps: Remove heap-helpers code
>   dma-buf: heaps: Skip sync if not mapped
>   dma-buf: system_heap: Allocate higher order pages if available
>
> If we talk about the last two patches - the ones that add system
> uncached heap, I somewhat agree that we should be able to show the
> performance gains with this approach (which has been in use on ION and
> in devices) using dma-buf gralloc or similar.
>
> We can discuss the system-uncached heap when the dma-buf gralloc or
> similar demonstration for performance benefits is done, but I am
> inclined to push these 5 patches listed above through.

Yeah makes total sense - I was arguing about the new stuff, not the refactoring.
-Daniel

>
> Best,
> Sumit.
>
> > -Daniel
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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